1. Technical Field
The present invention relates to a latching relay system equipped with a latching relay or latching relays.
2. Description of the Related Art
Common relays have only one mechanically stable state that is established by the force of a spring or the like. Therefore, to maintain another state (the electric contact is on or off) to which switching has been made from the stable state, it is necessary to generate electromagnetic force continuously by continuing to energize an electric coil of a relay.
On the other hand, in general, latching relays include a permanent magnet and a control electric coil and have a function of maintaining, on their own, a state of an electric contact. That is, since they have two stable states, switching is made to another stable state (the electric contact is on or off) merely by energizing an electric coil temporarily.
When latching relays are used, the power consumption can be made much smaller than in the case of using common relays because it is not necessary to energize the electric coil continuously in the latching relays. Therefore, the latching relays could be used in various uses such as vehicular devices.
Incidentally, in a case where plural components that handle magnetism such as relays are installed, a problem of interference between adjoining components may occur.
JP-A-2-270246 discloses a circuit breaker for reducing the influence of electromagnetic force between adjoining components. More specifically, the circuit breaker is configured in such a manner that each of such components as coils is surrounded by a magnetic shield plate that is made of a magnetic material.
For example, it is conceivable to switch vehicular relays from common relays to latching relays to reduce power consumption. In this case, since a large number of relays need to be installed in a vehicle, it is required to arrange a large number of latching relays in a small space by making the components mounting density as high as possible.
However, where plural latching relays are arranged close to each other, occurrence of mutual interference is highly probable. More specifically, the magnetism of a permanent magnet that is incorporated in a latching relay affects an operation of another, adjacent latching relay. As a result, the voltage (called a switching voltage) to be applied to each electric coil to switch the state of the latching relay rises or lowers.
If the switching voltage of a latching relay becomes higher than a rated value in this manner, the probability of occurrence of an operation failure in the latching relay increases. In particular, in the case of vehicular uses, the power source voltage may drop temporarily by an abnormally large value with such timing as a start of the engine, possibly resulting in an operation failure.
In common relays which are energized continuously, even if an operation failure occurs, the relay recovers from it immediately upon recovery of the power source voltage. In contrast, in latching relays in which the electric coil is energized only at the time of state switching, the abnormal state of an operation failure may last for a long time.
It is therefore conceivable to employ, for example, the circuit breaker as disclosed in JP-A-2-270246 and surround each latching relay by a magnetic shield plate. However, since magnetic shield plates are generally made of iron, the device is unavoidably increased in weight and becomes expensive. Furthermore, this is an obstruction to increase of mounting density.
In the case of vehicular uses, the power source voltage may drop temporarily by an abnormally large value with such timing as a start of the engine, the switching voltage is desired to be as low as possible even in a case that only a single latching relay is used. That is, so that no operation failure occurs even in a situation of an abnormal drop of the power source voltage, it is desired that the state of a latching relay be switched reliably by applying a low voltage to the electric coil.
The present invention has been made in the above circumstances, and an object of the present invention is to provide a latching relay system in which a reliable operation is expected even with a relatively low voltage in driving a latching relay and which contributes to increase of the mounting density of plural components.